Position detection system and projection display system

ABSTRACT

An optical position detection system includes a light output unit that outputs lights toward a first detection target and a second detection target, and a first light receiving unit that receives a first reflected light from the first detection target and a second light receiving unit that receives a second reflected light from the second detection target having different wavelengths, wherein the first detection target has a first reflection filter that reflects the first reflected light and the second detection target has a second reflection filter that reflects the second reflected light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 13/417,627 filedMar. 12, 2012 which claims priority to Japanese Patent Application No.2011-055185 filed Mar. 14, 2011, all of which are expressly incorporatedby reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a position detection system thatoptically detects a position of a detection target and a projectiondisplay system.

2. Related Art

In the past, position detection systems like touch panels have been usedfor electronic devices with display screen such as cellular phones, carnavigation systems, automated ticket vending machines, and automatedteller machines. The position detection system is provided at the visualrecognition side of the display screen and detects a position of adetection target like a pen or a finger by placing the detection targeton the display screen while referring to an image on the display screen.For example, they are disclosed in Patent Document 1 (U.S. Pat. No.5,666,037) and Patent Document 2 (U.S. Pat. No. 6,927,384).

The position detection systems disclosed in Patent Document 1 and PatentDocument 2 are optical systems, and each has a detection space set on areference surface of a body surface and includes a light source and alight detection unit. When a detection target is placed in an arbitraryposition within the detection space, the light of the light source isreflected on the surface of the detection target and a part of thereflected light is received by the light detection unit, and thereby,the position of the detection target is detected.

However, in the position detection systems disclosed in Patent Document1 and Patent Document 2, if two detection targets are placed at the sametime within the detection space, the light detection unit may notrespectively distinguish the reflected lights of the two detectiontargets, but may detect the intermediate position between the twodetection targets. Accordingly, there has been a problem that it may beimpossible to detect the respective positions of the two detectiontargets.

SUMMARY

An advantage of some aspects of the invention is to provide an opticalposition detection system that may detect respective positions of pluraldetection targets.

Application Example 1

This application example is directed to a position detection systemincluding a light output unit that outputs lights toward a firstdetection target and a second detection target, a light receiving unitthat receives lights reflected from the first detection target and thesecond detection target, and a position detection unit that detectspositions of the first detection target and the second detection targetusing the lights received by the light receiving unit, wherein the firstdetection target has a first reflection filter that reflects a firstreflected light and the second detection target has a second reflectionfilter that reflects a second reflected light having a differentwavelength from that of the first reflected light, and the lightreceiving unit has a first light receiving unit that detects the firstreflected light and a second light receiving unit that detects thesecond reflected light by distinguishing wavelengths of the lights.

According to the application example, the light output unit outputslights toward the first detection target and the second detectiontarget. The first detection target has the first reflection filter thatreflects the first reflected light and the second detection target hasthe second reflection filter that reflects the second reflected lighthaving the different wavelength from that of the first reflected light.Thereby, the first reflected light and the second reflected light arelights having different wavelengths.

Further, the first reflected light of the lights output from the lightoutput unit is reflected by the first detection target. Then, the firstreceiving unit distinguishes the wavelength of the reflected light andreceives the first reflected light. Thereby, the position of the firstdetection target can be detected by the position detection unit.Similarly, the second reflected light of the lights output from thelight output unit is reflected by the second detection target. Then, thesecond receiving unit distinguishes the wavelength of the reflectedlight and receives the second reflected light. Thereby, the position ofthe second detection target can be detected by the position detectionunit. Therefore, the optical position detection system may respectivelydistinguish and detects the position of the first detection target andthe position of the second detection target.

Application Example 2

In the position detection system according to the application example,it is preferable that the first reflection filter and the secondreflection filter each has a frequency filter and a retroreflector thatreflects incident light in an opposite direction to an incidentdirection.

According to this application example, the first reflected light to bereflected by the first detection target and the second reflected lightto be reflected by the second detection target may distinctly be set atdifferent frequencies by the frequency filters. Further, since theretroreflector reflects the reflected light in a predetermineddirection, the reflected light for detection of the position mayefficiently be received. Therefore, the positions of the pluraldetection targets may be accurately detected.

Application Example 3

In the position detection system according to the application example,it is preferable that the retroreflector has a prism shape.

According to this application example, the retroreflector has the prismshape. The prism shape is a shape having two sides at a right angle inthe sectional shape. In this regard, the prism shape may efficiently andreliably bring incident light into reflected light in parallel in theopposite direction.

Application Example 4

In the position detection system according to the application example,it is preferable that the frequency filter is provided by coating orbonding on a surface of the retroreflector.

According to this application example, there is no air layer between thefrequency filter and the retroreflector, and the lights from the lightoutput unit are not deteriorated by interface reflection. As a result,the individual differences in reflectance due to manufacturingvariations of the detection targets may be made smaller.

Application Example 5

In the position detection system according to the application example,it is preferable that the first light receiving unit and the secondlight receiving unit are provided in one photodetector.

According to this application example, the first light receiving unitand the second light receiving unit are provided in one photodetector.Accordingly, compared to the case where they are separately provided,the number of parts may be reduced. Furthermore, adjustment of thedirections in which the first light receiving unit and the second lightreceiving unit receive lights may be made easier. Therefore, thedifference in directionality between the light receiving units may bereduced and the influence on position information by the displacement ofthe detection positions may be reduced. As a result, the relativepositions of the respective detection targets may be accurately detectedwithout complicated processing.

Application Example 6

In the position detection system according to the application example,it is preferable that an angle formed by a line connecting the lightoutput unit and the first detection target and a line connecting thephotodetector and the first detection target is 10 degrees or less, andan angle formed by a line connecting the light output unit and thesecond detection target and a line connecting the photodetector and thesecond detection target is 10 degrees or less.

According to this application example, the angle formed by the lineconnecting the light output unit and the first detection target and theline connecting the photodetector and the first detection target is 10degrees or less. Further, the angle formed by the line connecting thelight output unit and the second detection target and the lineconnecting the photodetector and the second detection target is 10degrees or less. Since the retroreflectors have the properties ofreflecting incident light in parallel in the opposite direction, if theangles formed by the lines connecting the light output unit and thefirst detection target and the second detection target and the linesconnecting the photodetector and the first detection target and thesecond detection target are more than 10 degrees, the amount of lightreceived by the light receiving units becomes smaller and insufficientfor position detection. In the application example, the photodetectorsare provided in the locations where the reflected lights can bereceived. Therefore, the photodetectors may efficiently receive thelights formed by reflection of the lights from the light output unit bythe first detection target and the second detection target.

Application Example 7

This application example is directed to a projection display systemincluding the position detection system and an image irradiation systemthat projects an image on a reference surface.

The projection display system includes the image irradiation system thatprojects an image on the reference surface. Therefore, the imageprojected on the reference surface may be viewed. Further, theprojection display system includes the optical position detectionsystem. Therefore, a system combining an image and a function ofdetecting the first detection target and the second detection target maybe constructed. In this case, the light output unit may be provided inthe image irradiation system, or separately from the image irradiationsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view showing a configuration of aposition detection system.

FIG. 2 is a schematic side view showing the configuration of theposition detection system.

FIG. 3 is a schematic front view showing the configuration of theposition detection system.

FIG. 4 is a schematic perspective view showing a configuration of alight output unit.

FIG. 5 is a circuit diagram showing a circuit configuration of a lightsource drive unit.

FIG. 6 is a distribution graph showing a frequency distribution oflights output by the light output unit.

FIG. 7 is a distribution graph showing a frequency distribution oflights output by the light output unit.

FIG. 8 is a schematic diagram showing a structure of a detection target.

FIG. 9 is a schematic sectional view showing a basic configurationexample of a retroreflector.

FIGS. 10A to 10H are schematic diagrams showing examples of shapes ofretroreflection element layers.

FIG. 11A shows reflection characteristics of a retroreflector of a firstreflection filter, and FIG. 11B shows reflection characteristics of aretroreflector of a second reflection filter.

FIG. 12A shows a frequency distribution of a first reflected light, andFIG. 12B shows a frequency distribution of a second reflected light.

FIG. 13 is a block diagram showing a configuration of a positiondetection unit.

FIGS. 14A to 14C are schematic diagrams for explanation of intensitydistributions of position detection lights and processing in theposition detection unit.

FIG. 15 is a schematic circuit diagram showing an example of a signalprocessing circuit of a first position detection part.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Next, embodiments of an optical position detection system according tothe invention will be explained with reference to the drawings. Thefollowing embodiments are application of the optical position detectionsystem to a projection display system, however, the invention may beapplied not only to the projection display system but also to variousdisplay systems and other various operation systems. Further, in thefollowing respective drawings, the respective members are shown inrecognizable sizes indifferent scaling relations from the real scalingrelations of the respective members.

Embodiment 1 Overall Configuration of Position Detection System

FIG. 1 is a schematic perspective view showing a configuration of aposition detection system, and FIG. 2 is a schematic side view showingthe configuration of the position detection system. FIG. 3 is aschematic front view showing the configuration of the position detectionsystem. As shown in FIGS. 1 to 3, the position detection system 1000according to the invention includes a first detection target 31 and asecond detection target 32 as targets of position detection, and a lightoutput unit 20 that outputs lights toward the first detection target 31and the second detection target 32. The position detection system 1000further includes a photodetector 30 as a position detection unit thatreceives respective reflected lights (a first reflected light 41 and asecond reflected light 42) of the first detection target 31 and thesecond detection target 32. A projection display system 1100 includesthe optical position detection system 1000 and an image irradiationsystem 1200 that projects an image on a reference surface.

Note that, for convenience of explanation, in FIGS. 1 to 3, the X-axisand Y-axis are set along the reference surface 10 and the Z-axis is setalong the normal direction of the reference surface 10. These X-axis,Y-axis, and Z-axis intersect one another.

The image irradiation system 1200 projects an image on the referencesurface 10. Thereby, when an operator 11 views the reference surface 10,the image projected on the reference surface 10 can be viewed. Further,the operator 11 grasps the first detection target 31 and the seconddetection target 32. The operator 11 designates specific locations ofthe projected images using the first detection target 31 and the seconddetection target 32. The light output unit 20 outputs lights into adetection space 70 set in parallel to the reference surface 10. Further,when the first detection target 31 and the second detection target 32are located in the detection space 70, the first detection target 31 andthe second detection target 32 are irradiated with the lights output bythe light output unit 20.

As shown in FIG. 3, a first reflection filter 61 is provided on thefirst detection target 31. Further, the irradiated light reflected bythe first reflection filter 61 is referred to as “first reflected light41”. A second reflection filter 62 is provided on the second detectiontarget 32. Further, the irradiated light reflected by the secondreflection filter 62 is referred to as “second reflected light 42”. Thefirst reflection filter 61 and the second reflection filter 62 havefunctions of reflecting lights having different wavelengths. Therefore,the first reflected light 41 and the second reflected light 42 havedifferent wavelengths.

In the photodetector 30, a first light receiving unit 51 that detectsthe first reflected light 41 and a second light receiving unit 52 thatdetects the second reflected light 42 are provided. Accordingly, thephotodetector 30 can distinguish and detect the first reflected light 41and the second reflected light 42. Further, the first light receivingunit 51 and the second light receiving unit 52 are provided in onephotodetector. Accordingly, compared to the case where they areseparately provided, the number of parts may be reduced. Furthermore,adjustment of the directions in which the first light receiving unit 51and the second light receiving unit 52 receive lights may be madeeasier. Therefore, the difference in directionality between the lightreceiving units may be reduced and the influence on position informationby the displacement of the detection positions may be reduced. As aresult, the relative positions of the respective detection targets maybe accurately detected without complicated processing.

FIG. 4 is a schematic perspective view showing a configuration of thelight output unit. As shown in FIG. 4, the light output unit 20 hasplural light emitting devices 90 that output infrared lights and a lightsource drive unit 100 that drives the plural light emitting devices 90.The light emitting devices 90 are LEDs (light emitting diodes), forexample, and position detection lights 80 are output from the plurallight emitting devices 90. The light output unit 20 that outputs lightstoward the first detection target 31 and the second detection target 32forms an intensity distribution of the position detection lights 80within the detection space 70.

FIG. 5 is a circuit diagram showing a circuit configuration of the lightsource drive unit. As shown in FIG. 5, the light source drive unit 100includes a light source drive circuit 110 that drives the plural lightemitting devices 90, and a light source control part 120 thatrespectively control the light emission intensity of the plural lightemitting devices 90 via the light source drive circuit 110. Of them, thelight source drive circuit 110 includes a first reflection light sourcedrive circuit 111, a second reflection light source drive circuit 112, athird reflection light source drive circuit 113, and a fourth reflectionlight source drive circuit 114, for example, and they are electricallyconnected to the respective one light emitting device 90. Thereby, theposition detection lights 80 are lights in a predetermined wavelengthrange. FIG. 6 is a distribution graph showing a frequency distributionof lights output by the light output unit. In FIG. 6, a positiondetection light distribution line 83 shows an example of thedistribution of the wavelengths of the position detection lights 80. Asshown by the position detection light distribution line 83, for example,the position detection lights 80 are lights in the wavelength range fromabout 800 nm to 1000 nm. Note that the position detection lights 80 haveone peak intensity in the wavelength range equal to or less than 900 nm.

Further, FIG. 7 is a distribution graph showing a frequency distributionof lights output by the light output unit. In FIG. 7, a positiondetection light distribution line 84 shows an example of thedistribution of the wavelengths of the position detection lights 80. Asshown by the position detection light distribution line 84, thefrequency distribution of the position detection lights 80 may be theposition detection light distribution line 84 obtained bysynchronization of two infrared light distribution lines 81, 82 havingdifferent wavelength ranges from each other. For example, one infraredlight distribution line 81 shows a distribution of lights in awavelength range from about 800 nm to about 900 nm, and the otherinfrared light distribution line 82 shows a distribution of lights in awavelength range from about 900 nm to about 1000 nm. Accordingly, theentire wavelength range is from about 800 nm to about 1000 nm, and hasrespective peak intensity in different wavelength ranges.

Thereby, compared to the case where the position detection lights areformed from one of the infrared light distribution line 81 and theinfrared light distribution line 82, in the position detection lights 80of the position detection light distribution line 84, the wavelengthrange of the position detection lights may be made wider and the lightintensity may be sufficiently provided in the separate wavelength rangesfrom each other. The position detection lights 80 may be generated byproviding respective plural first light emitting devices like LEDs thatoutput the infrared light distribution line 81 and second light emittingdevices like LEDs that output the infrared light distribution line 82 inthe light output unit 20 of the position detection system and lightingthem at the same time. Note that the position detection lights 80 may begenerated using three or more kinds of light emitting devices havingrespective different wavelength ranges.

FIG. 8 is a schematic diagram showing a structure of the detectiontarget. As shown in FIG. 8, the first detection target 31 and the seconddetection target 32 are respectively pen-shaped. Further,retroreflectors 130 are provided on the first detection target 31 andthe second detection target 32. The retroreflectors 130 may be providedon the surfaces of the first detection target 31 and the seconddetection target 32, and provided to cover the whole bodies. They arenecessary to be provided in locations irradiated with the positiondetection lights 80.

FIG. 9 is a schematic sectional view showing a basic configurationexample of the retroreflector. As shown in FIG. 9, the retroreflector130 includes a retroreflection element layer 140 and a surfaceprotective layer with frequency filter 150 as a frequency filter isprovided on one surface of the retroreflection element layer 140. Thesurface on which the surface protective layer with frequency filter 150is provided is a surface that the position detection lights 80 enter.The surface protective layer with frequency filter 150 provided in thefirst reflection filter 61 is referred to as “first frequency filter151” and the surface protective layer with frequency filter 150 providedin the second reflection filter 62 is referred to as “second frequencyfilter 152”. The first frequency filter 151 and the second frequencyfilter 152 have different frequency characteristics.

The surface protective layer with frequency filter 150 is provided onthe surface of the retroreflector 130 by coating or bonding. Thereby,there is no air layer between the surface protective layer withfrequency filter 150 and the retroreflector 130, and the lights from thelight output unit are not deteriorated by interface reflection. As aresult, the individual differences in reflectance due to manufacturingvariations of the detection targets may be made smaller.

In the retroreflection element layer 140, a hollow portion 141 isprovided at the opposite side to the surface protective layer withfrequency filter 150. Further, the lights are reflected by thedifference in refractive index between the retroreflection element layer140 and the hollow portion 141.

FIGS. 10A to 10H are schematic diagrams showing examples of shapes ofthe retroreflection element layers. FIG. 10A is a schematic plan viewshowing a retroreflection element layer of a first example, and FIG. 10Bis a schematic sectional view showing the retroreflection element layerof the first example. As shown in FIGS. 10A and 10B, the retroreflectionelement layer 142 includes a retroreflection element having a triangularpyramid corner cube shape. FIG. 10C is a schematic plan view showing aretroreflection element layer of a second example, and FIG. 10D is aschematic sectional view showing the retroreflection element layer ofthe second example. As shown in FIGS. 10C and 10D, the retroreflectionelement layer 143 includes a retroreflection element having a hexagonalprism shape.

FIG. 10E is a schematic plan view showing a retroreflection elementlayer of a third example, and FIG. 10F is a schematic sectional viewshowing the retroreflection element layer of the third example. As shownin FIGS. 10E and 10F, the retroreflection element layer 144 includes aretroreflection element having a triangular pyramid corner cube shape.FIG. 10G is a schematic plan view showing a retroreflection elementlayer of a fourth example, and FIG. 10H is a schematic sectional viewshowing the retroreflection element layer of the fourth example. Asshown in FIGS. 10G and 10H, the retroreflection element layer 145includes a retroreflection element having a hexagonal prism shape. Theretroreflection element layer 142 to the retroreflection element layer145 have properties of reflecting incident light in parallel in theopposite direction by these shapes.

This retroreflector 130 provided on the first detection target 31 isprovided with the first frequency filter 151 and the retroreflector 130provided on the second detection target 32 is provided with the secondfrequency filter 152, and the first frequency filter 151 and the secondfrequency filter 152 have different reflection characteristics from eachother.

It is preferable that the angle formed by the line connecting the lightoutput unit 20 and the first detection target 31 and the line connectingthe photodetector 30 and the first detection target 31 is 10 degrees orless. Similarly, it is preferable that the angle formed by the lineconnecting the light output unit 20 and the second detection target 32and the line connecting the photodetector 30 and the second detectiontarget 32 is 10 degrees or less. Since the retroreflectors 130 have theproperties of reflecting incident light in parallel in the oppositedirection, if the angles formed by the lines connecting the light outputunit 20 and the first detection target 31 and the second detectiontarget 32 and the lines connecting the photodetector 30 and the firstdetection target 31 and the second detection target 32 are 10 degrees ormore, the amount of light received by the photodetector 30 becomessmaller and insufficient for position detection. By providing thephotodetector 30 in the location where the reflected lights can bereceived, the photodetector 30 may efficiently receive the lights formedby reflection of the lights from the light output unit 20 by the firstdetection target 31 and the second detection target 32 in parallel inthe opposite direction to the incident light.

FIG. 11A shows reflection characteristics of the retroreflector of thefirst reflection filter, and FIG. 11B shows reflection characteristicsof the retroreflector of the second reflection filter. In FIG. 11A, afirst frequency characteristic line 151 a shows filter characteristicsof the first frequency filter 151. As shown by the first frequencycharacteristic line 151 a, specifically, the first frequency filter 151has reflection characteristics such that the reflectance of thewavelength range from about 800 nm to about 900 nm (the first wavelengthrange) is higher than the reflectance of the wavelength range from about900 nm to about 1000 nm (the second wavelength range).

On the other hand, in FIG. 11B, a second frequency characteristic line152 a shows filter characteristics of the second frequency filter 152.As shown by the second frequency characteristic line 152 a,specifically, the second frequency filter 152 has reflectioncharacteristics such that the reflectance of the wavelength range fromabout 900 nm to about 1000 nm is higher than the reflectance of thewavelength range from about 800 nm to about 900 nm.

FIG. 12A shows a frequency distribution of the first reflected light,and FIG. 12B shows a frequency distribution of the second reflectedlight. A position detection light distribution line 80 a shows afrequency distribution of the position detection lights 80. A firstreflected light distribution line 41 a shows a frequency distribution ofthe first reflected lights 41, and a second reflected light distributionline 41 a shows a frequency distribution of the second reflected lights42. As shown in FIG. 12A, when the position detection lights 80 enterthe first frequency filter 151, the light components of the positiondetection lights 80 in the wavelength range from about 900 nm to about1000 nm are absorbed by the first frequency filter 151, and the lightcomponents of the position detection lights 80 in the wavelength rangefrom about 800 nm to about 900 nm are reflected by the retroreflector130 and output as the first reflected lights 41.

As shown in FIG. 12B, when the position detection lights 80 enter thesecond frequency filter 152, the light components of the positiondetection lights 80 in the wavelength range from about 800 nm to about900 nm are absorbed by the second frequency filter 152, and the lightcomponents of the position detection lights 80 in the wavelength rangefrom about 900 nm to about 1000 nm are reflected by the retroreflector130 and output as the second reflected lights 42. Therefore, the firstreflected lights 41 of the first detection target 31 and the secondreflected lights 42 of the second detection target 32 have differentwavelength distributions from each other.

Configuration of Position Detection Unit

As shown in FIGS. 1 to 3, in the photodetector 30, the first lightreceiving unit 51 (first light detection unit) and the second lightreceiving unit 52 (second light detection unit) are provided within thesame casing. FIG. 13 is a block diagram showing a configuration of theposition detection unit. As shown in FIG. 13, a first reflected lightdetection part 511 is provided in the first light receiving unit 51 anda second reflected light detection part 521 is provided in the secondlight receiving unit 52. In the photodetector 30, a first positiondetection part 512 that obtains position information based on adetection value of the first reflected light detection part 511 and asecond position detection part 522 that obtains position informationbased on a detection value of the second reflected light detection part521 are provided.

These first reflected light detection part 511 and second reflectedlight detection part 521 have different sensitivity characteristics fromeach other. Specifically, the first reflected light detection part 511has sensitivity characteristics such that the detection sensitivity ofthe wavelength range from about 800 nm to about 900 nm is higher thanthe detection sensitivity of the wavelength range from about 900 nm toabout 1000 nm. Thereby, the influence of the second reflected light 42on the detection value of the first reflected light detection part 511may be made smaller and the detection value reflecting the intensity ofthe first reflected light 41 may be obtained. The first reflected lightdetection part 511 is electrically connected to the first positiondetection part 512, and the detection value of the first reflected lightdetection part 511 is output to the first position detection part 512.

On the other hand, the second reflected light detection part 521 hassensitivity characteristics such that the detection sensitivity of thewavelength range from about 900 nm to about 1000 nm is higher than thedetection sensitivity of the wavelength range from about 800 nm to about900 nm. Thereby, the influence of the first reflected light 41 on thedetection value of the second reflected light detection part 521 may bemade smaller and the detection value reflecting the intensity of thesecond reflected light 42 may be obtained. The second reflected lightdetection part 521 is electrically connected to the second positiondetection part 522, and the detection value of the second reflectedlight detection part 521 is output to the second position detection part522.

Therefore, the first position detection part 512 of the first lightreceiving unit 51 may detect the position of the first detection target31 in the detection space 70 using the detection value of the firstreflected light detection part 511 detecting the first reflected light41 and the intensity distribution of the position detection lights 80.Further, the second position detection part 522 of the second lightreceiving unit 52 may detect the position of the second detection target32 in the detection space 70 using the detection value of the secondreflected light detection part 521 detecting the second reflected light42 and the intensity distribution of the position detection lights 80.

Basic Principle of Coordinate Detection

In the optical position detection system of the embodiment, theintensity distribution of the position detection lights 80 is formedalong the reference surface 10 in the detection space 70 by lighting theplural light emitting devices 90 of the light output unit 20. Under thecondition, the first reflected light 41 reflected by the retroreflector130 of the first detection target 31 is detected by the first reflectedlight detection part 511 and the position of the first detection target31 in the detection space 70 is detected by the first position detectionpart 512 based on the result. Further, the second reflected light 42reflected by the retroreflector 130 of the second detection target 32 isdetected by the second reflected light detection part 521 and theposition of the second detection target 32 in the detection space 70 isdetected by the second position detection part 522 based on the result.As below, the configuration of the light intensity distribution and theprinciple of coordinate detection of the first detection target 31 willbe explained with reference to FIGS. 14A to 14C. Note that thecoordinate detection principle of the second detection target 32 is thesame as the principle of the coordinate detection of the first detectiontarget 31, and the explanation will be omitted.

FIGS. 14A to 14C are schematic diagrams for explanation of intensitydistributions of position detection lights and processing in theposition detection unit. FIG. 14A is a diagram for explanation of anintensity distribution of the position detection lights in the X-axisdirection, FIG. 14B is a diagram for explanation of intensity ofreflected lights reflected by the first detection target, and FIG. 14Cis a diagram for explanation of adjustment of the intensity distributionof the position detection lights so that the intensity of the reflectedlights reflected by the first detection target are equal.

When the position detection lights 80 are output from the light outputunit 20, the intensity distribution of the position detection lights 80is formed along the reference surface 10 in the detection space 70according to the lighting pattern of the plural light emitting devices90. For example, when the X-coordinate is detected, as shown in FIG. 14Aand FIG. 14B, first, a first intensity distribution for X-coordinatedetection 80Xa in which intensity gradually decreases from one side X1toward the other side X2 in the X-axis direction is formed in a firstperiod, and then, a second intensity distribution for X-coordinatedetection 80Xb in which the intensity gradually decreases from the otherside X2 toward the one side X1 in the X-axis direction is formed in asecond period.

Here, as shown in the example, it is preferable that the first intensitydistribution for X-coordinate detection 80Xa in which the intensitylinearly decreases from the one side X1 toward the other side X2 in theX-axis direction is formed in the first period, and the second intensitydistribution for X-coordinate detection 80Xb in which the intensitylinearly decreases from the other side X2 toward the one side X1 in theX-axis direction is formed in the second period.

Under the condition, when the first detection target 31 is placed in thedetection space 70, the position detection light 80 is reflected by theretroreflector 130 of the first detection target 31 and modulated intothe first reflected light 41, and a part of the first reflected light 41is detected by the first reflected light detection part 511 of thephotodetector 30. In this regard, if the first intensity distributionfor X-coordinate detection 80Xa and the second intensity distributionfor X-coordinate detection 80Xb are set in advance, the X-coordinate ofthe first detection target 31 may be detected by the following method orthe like.

As shown in FIG. 14B, the first method is a method of using thedifference between the first intensity distribution for X-coordinatedetection 80Xa and the second intensity distribution for X-coordinatedetection 80Xb. Specifically, the first intensity distribution forX-coordinate detection 80Xa and the second intensity distribution forX-coordinate detection 80Xb are adapted to have predetermineddistribution forms set in advance, and the difference between the firstintensity distribution for X-coordinate detection 80Xa and the secondintensity distribution for X-coordinate detection 80Xb is also afunction of the X-coordinate in the form set in advance. Therefore, byobtaining the difference between a detection value 300Xa in the firstreflected light detection part 511 when the first intensity distributionfor X-coordinate detection 80Xa is formed in the first period and adetection value 300Xb in the first reflected light detection part 511when the second intensity distribution for X-coordinate detection 80Xbis formed in the second period, the X-coordinate of the first detectiontarget 31 may be detected. Note that the ratio between the detectionvalues 300Xa and 300Xb is also a function of the X-coordinate, and theX-coordinate can be detected by obtaining the ratio.

The second method is a method of using an amount of adjustment when thedrive currents of the plural light emitting devices 90 are adjusted sothat the detection value 300Xa in the first intensity distribution forX-coordinate detection 80Xa and the detection value 300Xb in the secondintensity distribution for X-coordinate detection 80Xb may be equal.Note that the second method may be applied to the case where the firstintensity distribution for X-coordinate detection 80Xa and the secondintensity distribution for X-coordinate detection 80Xb linearly changewith respect to the X-coordinate as shown in FIG. 14B.

As shown in FIG. 14B, first, in the first period and the second period,the first intensity distribution for X-coordinate detection 80Xa and thesecond intensity distribution for X-coordinate detection 80Xb are formedto have equal absolute values in opposite directions along the X-axis.Under the condition, if the detection value 300Xa in the first intensitydistribution for X-coordinate detection 80Xa and the detection value300Xb in the second intensity distribution for X-coordinate detection80Xb are equal, it is known that the first detection target 31 islocated at the center in the X-axis direction.

On the other hand, as shown in FIG. 14C, when the detection value 300Xaand the detection value 300Xb are different, the drive currents for theplural light emitting devices 90 are adjusted in both or one of thefirst period and the second period to make them equal, and, again, thefirst intensity distribution for X-coordinate detection 80Xa is formedin the first period and the second intensity distribution forX-coordinate detection 80Xb in the second period. As a result, if thedetection value 300Xa and the detection value 300Xb become equal, theX-coordinate of the first detection target 31 may be detected from theratio, the difference, or the like between an amount of adjustmentΔ300Xa in the first period and an amount of adjustment Δ300Xb in thesecond period. Alternatively, the X-coordinate of the first detectiontarget 31 may be detected from the ratio, the difference, or the likebetween an amount of control with respect to the plural light emittingdevices 90 in the first period after adjustment and an amount of controlwith respect to the plural light emitting devices 90 in the secondperiod after adjustment.

In either case where the first method or the second method is employed,similarly, a first intensity distribution for Y-coordinate detection inwhich intensity gradually decreases from one side toward the other sidein the Y-axis direction is formed in a third period. Then, a secondintensity distribution for Y-coordinate detection in which the intensitygradually decreases from the other side toward the one side in theY-axis direction is formed in a fourth period. Thereby, the Y-coordinateof the first detection target 31 may be detected. Further, if anintensity distribution in the Z-axis direction is formed in a fifthperiod, the Z-coordinate of the first detection target 31 may bedetected. Here, in the fifth period, for example, all of the lightemitting devices 90 of the light output unit 20 are driven in the sameamount of light emission, and thereby, an intensity distribution inwhich the intensity is nearly constant in the X-axis and Y-axisdirections, but the intensity changes in the Z-axis direction may beformed. Note that the X-coordinate, the Y-coordinate, and theZ-coordinate of the second detection target 32 may respectively bedetected using the first method and the second method in the samemanner.

Further, in either method of the first method and the second method,even if an infrared component contained in environment light enters thefirst reflected light detection part 511, when the difference betweenthe detection values 300Xa and 300Xb is obtained or the detection values300Xa and 300Xb are adjusted to be equal, the intensity of theenvironment light is cancelled out, and thus, the environment light hasno influence on the detection accuracy of the first detection target 31.Even if the environment light enters the second reflected lightdetection part 521, similarly, it has no influence on the detectionaccuracy of the second detection target 32.

As described above, the position information of the first detectiontarget 31 in the detection space 70 is acquired based on the detectionresult of the first reflected light detection part 511. Further, theposition information of the second detection target 32 in the detectionspace 70 is acquired based on the detection result of the secondreflected light detection part 521. In this regard, for example, aconfiguration of using micro processing units (MPUs) respectively forthe first position detection part 512 and the second position detectionpart 522 and performing processing according to execution ofpredetermined software (operation program) may be employed. Further, aswill be explained with reference to FIG. 15, a configuration ofperforming processing by a signal processing unit using hardware such asa logic circuit may be employed.

FIG. 15 is a schematic circuit diagram showing an example of a signalprocessing circuit of the first position detection part. The firstposition detection part 512 shown here realizes the first method in theabove described basic principle of coordinate detection. That is, thedifference between the detection value 300Xa in the first reflectedlight detection part 511 in the first period and the detection value300Xb in the first reflected light detection part 511 in the secondperiod is calculated. Then, the calculated difference value is checkedagainst the preset function value of the difference between the firstintensity distribution for X-coordinate detection 80Xa and the secondintensity distribution for X-coordinate detection 80Xb, and thereby, theX-coordinate of the first detection target 31 is detected. Note that theconfigurations for respectively detecting the X-coordinate, theY-coordinate, and the Z-coordinate of the first detection target 31 arethe same, and only the case of obtaining the X-coordinate of the firstdetection target 31 will be described in the following explanation.Further, the second reflected light detection part 521 and the secondposition detection part 522 of the second light receiving unit 52 fordetection of the X-coordinate, the Y-coordinate, and the Z-coordinate ofthe second detection target 32 shown in FIG. 13 are respectively thesame as the first reflected light detection part 511 and the firstposition detection part 512 of the first light receiving unit 51, andtheir explanation will be omitted.

As shown in FIG. 15, the light source drive circuit 110 in the positiondetection system 1000 of the embodiment is shown to apply drive pulsehaving a predetermined current value to the plural light emittingdevices 90 via a variable resister 160 in the first period, and applydrive pulse having a predetermined current value to the plural lightemitting devices 90 via a variable resister 161 and an inverting circuit170 in the second period. Therefore, the light source drive circuit 110applies drive pulse in the opposite phases to the plural light emittingdevices 90 in the first period and the second period.

Further, the position detection lights 80 when forming the firstintensity distribution for X-coordinate detection 80Xa in the firstperiod are reflected by the retroreflector 130 of the first detectiontarget 31 and modulated into the first reflected lights 41, and thefirst reflected lights 41 are received by the first reflected lightdetection part 511. Similarly, the position detection lights 80 whenforming the second intensity distribution for X-coordinate detection80Xb in the second period are reflected by the retroreflector 130 of thefirst detection target 31 and modulated into the first reflected lights41, and the first reflected lights 41 are received by the firstreflected light detection part 511. The first reflected light detectionpart 511 is provided in a light intensity signal generation circuit 180,and a resister 190 of about 1 kΩ is electrically series-connected and abias voltage Vb is applied to their ends.

In the light intensity signal generation circuit 180, the first positiondetection part 512 is electrically connected to a connection point 200between the first reflected light detection part 511 and the resister190. A detection signal Vc output from the connection point 200 is analternating-current signal in response to the pulse signal having alevel and an amplitude reflecting the light intensity received by thefirst reflected light detection part 511.

The first position detection part 512 is connected to the output of thelight intensity signal generation circuit 180. The first positiondetection part 512 has a signal extraction circuit 220 that extracts alight detection signal, a signal extraction circuit 260 that separatessignals in the first period and the second period from the lightdetection signal, and a signal processing circuit 300 that forms asignal relating to the position information based on the separatedsignals.

The signal extraction circuit 220 includes a filter 230 having acapacitor of about 1 nF, and the filter 230 functions as a high-passfilter that removes a direct-current component from the signal outputfrom the connection point 200 between the first reflected lightdetection part 511 and the resister 190. Accordingly, from the detectionsignal Vc output from the connection point 200 by the filter 230, aposition detection signal Vd as an alternating-current component of thevoltage Vc is extracted. That is, while the position detection lights 80are modulated, the environment light may be regarded constant inintensity within a certain period. Thus, the lower frequency componentsor the direct-current components due to the environment light areremoved by the filter 230.

Further, the signal extraction circuit 220 has an adder circuit 250including a feedback resister 240 of about 220 kΩ at the downstream ofthe filter 230. The position detection signal Vd extracted by the filter230 is output to the signal extraction circuit 260 as a positiondetection signal Vs formed by superimposition on the voltage V/2 as ahalf of the bias voltage Vb.

The signal extraction circuit 260 includes a switch 270 that performsswitching operation in synchronization with the drive pulse applied tothe light emitting devices 90 in the first period, a comparator 280, andcapacitors 290 respectively electrically connected to input lines of thecomparator 280. Accordingly, when the position detection signal Vs isinput to the signal extraction circuit 260, an effective value Vea ofthe position detection signal Vs in the first period and an effectivevalue Veb of the position detection signal Vs in the second period arealternately output from the signal extraction circuit 260 to the signalprocessing circuit 300.

The signal processing circuit 300 obtains a difference between theeffective value Vea in the first period and the effective value Veb inthe second period, and outputs the difference to a positiondetermination unit 310 as a position detection signal Vg. In a memorypart 320 of the position determination unit 310, function values of thedifference between the first intensity distribution for X-coordinatedetection 80Xa and the second intensity distribution for X-coordinatedetection 80Xb along the X-axis direction in the detection space 70 areheld and the corresponding X-coordinate is determined by checking theposition detection signal Vg against the function value, and thereby,the X-coordinate of the first detection target 31 may be obtained.

Note that the second method in the above described basic principle ofcoordinate detection detects the X-coordinate of the first detectiontarget 31 based on the amount of adjustment when the amounts of control(drive currents) of the plural light emitting devices 90 are adjusted sothat the detection values 300Xa and 300Xb in the first reflected lightdetection part 511 in the first period and the second period may beequal. As shown by broken lines in FIG. 15, a control signal Vf isoutput from the signal processing circuit 300 of the first lightreceiving unit 51 to the light source drive circuit 110 of the positiondetection system 1000 so that the effective value Vea of the positiondetection signal Vs in the first period and the effective value Veb ofthe position detection signal Vs in the second period may be at the samelevel. In this case, the effective value Vea in the first period and theeffective value Veb in the second period are compared, and, if they areequal, the present drive condition is maintained. On the other hand, ifthe effective value Vea in the first period is lower than the effectivevalue Veb in the second period, the resistance value of the variableresister 160 is made lower and the amount of output lights from thelight emitting diodes 90 in the first period is made higher. Further, ifthe effective value Veb in the second period is lower than the effectivevalue Vea in the first period, the resistance value of the variableresister 161 is made lower and the amount of output lights in the secondperiod is made higher. Then, the amount of adjustment when the effectivevalues Vea and Veb are finally at the same level is used for calculationof the position information.

As described above, there are the following advantages according to theembodiment.

(1) In the embodiment, the first frequency filter 151 and the secondfrequency filter 152 having different reflection characteristics fromeach other are provided in the first detection target 31 and the seconddetection target 32, respectively. Further, the retroreflectors 130 thatstrongly reflect incident light in parallel in the opposite directionare provided and the first reflected light detection part 511 and thesecond reflected light detection part 521 having different sensitivitycharacteristics from each other are respectively provided in thephotodetector 30. Thereby, the detection value of the first reflectedlight detection part 511 reflects the reflected light (first reflectedlight 41) of the first frequency filter 151, but the influence of thereflected light (second reflected light 42) of the second frequencyfilter 152 is suppressed. Further, the detection value of the secondreflected light detection part 521 reflects the reflected light (secondreflected light 42) of the second frequency filter 152, but theinfluence of the reflected light (first reflected light 41) of the firstfrequency filter 151 is suppressed. Two reflected lights mayrespectively return strong reflected lights to the detector, and thus,the reflected lights of the first detection target 31 and the seconddetection target 32 may be distinguished without mixing up andaccurately detected. Therefore, the positions of the first detectiontarget 31 and the second detection target 32 in the detection space 70may respectively be detected.

(2) The first frequency filter 151 and the second frequency filter 152are provided at the ends of the first detection target 31 and the seconddetection target 32, respectively. Further, the first frequency filter151 passes the first reflected light 41 and the second frequency filter152 passes the second reflected light 42. The first light receiving unit51 detects the first reflected light 41 and the second light receivingunit 52 detects the second reflected light 42. Therefore, the firstlight receiving unit 51 may detect the position of the first detectiontarget 31 and the second light receiving unit 52 may detect the positionof the second detection target 32. Furthermore, the retroreflectors 130reflect the reflected lights in predetermined directions, and thereby,the reflected lights for detection of the positions may efficiently bereceived. Therefore, the positions of the plural detection targets mayaccurately be detected.

(3) In the embodiment, the retroreflector 130 has the prism shape. Inthis regard, the prism shape may efficiently and reliably bring incidentlight into reflected light in parallel in the opposite direction.

(4) In the embodiment, the surface protective layer with frequencyfilter 150 is provided by coating or bonding on the surface of theretroreflector 130. There is no air layer between the surface protectivelayer with frequency filter 150 and the retroreflector 130, and thelights from the light output unit 20 are not deteriorated by interfacereflection. As a result, the individual differences in reflectance dueto manufacturing variations of the detection targets may be madesmaller.

(5) In the embodiment, the first light receiving unit 51 and the secondlight receiving unit 52 are provided in one photodetector 30.Accordingly, compared to the case where they are separately provided,the number of parts may be reduced. Furthermore, adjustment of thedirections in which the first light receiving unit 51 and the secondlight receiving unit 52 receive lights may be made easier. Therefore,the difference in directionality between the light receiving units maybe reduced and the influence on position information by the displacementof the detection positions may be reduced. As a result, the relativepositions of the respective detection targets may accurately be detectedwithout complicated processing.

(6) In the embodiment, the angle formed by the line connecting the lightoutput unit 20 and the first detection target 31 and the line connectingthe photodetector 30 and the first detection target 31 is 10 degrees orless. Further, the angle formed by the line connecting the light outputunit 20 and the second detection target 32 and the line connecting thephotodetector 30 and the second detection target 32 is 10 degrees orless. Since the retroreflectors 130 have the properties of reflectingincident light in parallel in the opposite direction, if the anglesformed by the lines connecting the light output unit 20 and the firstdetection target 31 and the second detection target 32 and the linesconnecting the photodetector 30 and the first detection target 31 andthe second detection target 32 are more than 10 degrees, the amount oflights received by the photodetector 30 becomes smaller and insufficientfor position detection. In the embodiment, the photodetector 30 isprovided in the location where the reflected lights can be received.Therefore, the photodetector may efficiently receive the lights formedby reflection of the lights from the light output unit 20 by the firstdetection target 31 and the second detection target 32.

(7) In the embodiment, the reflected lights from the first detectiontarget 31 and the second detection target 32 may be made stronger by theretroreflectors 130. Therefore, even in the case where the display areais wider as in a projection display apparatus (projector), the positionscan optically be detected.

(8) In the embodiment, for detection of coordinates of the firstdetection target 31 and the second detection target 32, the first methodin the basic principle of coordinate detection, i.e., a method usingdifference between two kinds of intensity distributions of the positiondetection lights 80 may be used. The second method is the method usingthe amount of adjustment when the drive currents of the plural lightemitting devices 90 are adjusted so that the detection values in the twokinds of intensity distributions may be equal. In this regard, comparedto the second method, in the first method, it is not necessary to adjustthe drive currents of the plural light emitting devices 90 with respectto each of the first detection target 31 and the second detection target32. Accordingly, the positions of the first detection target 31 and thesecond detection target 32 may be detected in parallel at the same time.Therefore, time-sharing processing or the like is not necessary and theposition information of the plural detection targets can be obtained atarbitrary times, and thus, plural detection targets can be distinguishedusing a simple configuration.

(9) In the embodiment, the projection display system 1100 includes theimage irradiation system 1200 that projects an image on the referencesurface 10. Therefore, the image projected on the reference surface 10may be viewed. Further, the projection display system 1100 includes theposition detection system 1000. Therefore, a system combining an imageand a function of detecting the first detection target 31 and the seconddetection target 32 may be constructed. In this case, the light outputunit 20 may be provided in the image irradiation system 1200, orseparately from the image irradiation system 1200.

The invention is not limited to the above described illustratedexamples, but various changes may obviously be made without departingfrom the scope of the invention.

Modified Example 1

In the embodiment, the first frequency filter 151 and the secondfrequency filter 152 having different reflection characteristics fromeach other have been provided on the surfaces of the first detectiontarget 31 and the second detection target 32, respectively. Thedifferent reflection characteristics from each other may be provided notby providing the first frequency filter 151 and the second frequencyfilter 152, but by forming constituent materials exposed on the surfacesof the first detection target 31 and the second detection target 32using different materials.

Modified Example 2

In the embodiment, the first detection target 31 and the seconddetection target 32 and the corresponding first reflected lightdetection part 511 and second reflected light detection part 521 havebeen provided. Further, the positions of the first detection target 31and the second detection target 32 have been respectively detected usingdifferent wavelength ranges from each other. Not limited to the method,but three or more detection targets and three or more photodetectors areprovided and the positions of the three or more detection targets may berespectively detected using three or more different wavelength ranges.

The embodiment has been explained in detail, and the person who skilledin the art could easily understood that many modifications may be madewithout substantially departing from the new matter and effects of theinvention. Therefore, all of the modified examples are contained withinthe range of the invention. For example, in the specification and thedrawings, the terms written with the broader or synonymous differentterms at least once may be replaced by the different terms in anylocation of the specification and the drawings. Further, theconfigurations, operations of the optical position detection system andthe projection display system may not be limited to those explained inthe embodiment, but various modifications can be implemented.

What is claimed is:
 1. A position detection apparatus comprising: alight output unit that outputs light toward a first detection target anda second detection target; a first light receiving unit that receiveslight and detects, by distinguishing wavelengths of the light, a firstreflected light reflected by the first detection target; a second lightreceiving unit that receives light and detects, by distinguishingwavelengths of the light, a second reflected light reflected by thesecond detection target; and a position detection unit that detectspositions of the first detection target and the second detection targetbased on detection values of the first and second light receiving units.2. The position detection apparatus according to claim 1, wherein thefirst light receiving unit and the second light receiving unit areprovided in one photodetector.
 3. The position detection apparatusaccording to claim 2, wherein an angle formed by a line connecting thelight output unit and the first detection target and a line connectingthe photodetector and the first detection target is 10 degrees or less,and an angle formed by a line connecting the light output unit and thesecond detection target and a line connecting the photodetector and thesecond detection target is 10 degrees or less.
 4. A projection displaysystem comprising: the position detection system according to claim 1;and an image irradiation system that projects an image on a referencesurface.
 5. A light reflecting device for a position detection apparatuscomprising: a detection target that is held by a user's hand; and areflection filter on the detection target that reflects light having apredetermined wavelength.
 6. The light reflecting device according toclaim 5, wherein the reflection filter has a frequency filter and aretroreflector that reflects incident light in an opposite direction toan incident direction.
 7. The light reflecting device according to claim6, wherein the retroreflector has a prism shape.
 8. The light reflectingdevice according to claim 6, wherein the frequency filter is provided bycoating or bonding on a surface of the retroreflector.
 9. A methodcomprising: outputting light toward a first detection target and asecond detection target; detecting a first reflected light reflected bythe first detection target and a second reflected light reflected by thesecond detection target by distinguishing wavelengths of the lightreflected by the first and second detection targets; and detectingpositions of the first detection target and the second detection targetbased on a detection value of the received light.
 10. The method ofclaim 9 wherein: the first and second detection targets are holdable bya user's hand; and wherein: the first and second detection targetsreflect light of different wavelegnths.